(1) Field of the Invention
The present invention relates to an inexpensive reduction gears-integrated actuator that is capable of shortening the length of the entire actuator in its axial direction and increasing a drive torque without running counter to downsizing and lightening of its weight.
(2) Description of the Related Art
Conventionally, an actuator used for a robot, a machine tool, etc., in which harmonic reduction gears and an electric motor are integrated together is constructed as shown in FIG. 3.
FIG. 3 is a side sectional view of a prior art reduction gears-integrated actuator.
In the drawing, 30 denotes an actuator, 31a denotes a load side bracket, 31b, 31c and 31d denote actuator frames, 31e denotes an anti-load side bracket, 32 denotes an output shaft, 33 denotes a rotation shaft, 34 denotes an electric motor, 35 denotes astator, 36 denotes a stator core, 37 denotes an armature winding, 38 denotes a rotor, 39 denotes a yoke, 40 denotes a permanent magnet, 41 denotes harmonic reduction gears, 42 denotes a circular spline, 43 denotes a flexible spline, 44 denotes a wave generator, 45, 46, 4748, and 49 denote bearings, 50 and 51 denote elastic members, 52 denotes a rotation position detector, 53 denotes a rotation disk, 54 denotes a fixed slit, 55 denotes alight emitting element, 56 denotes a light receiving element, and L0 indicates a length of the actuator 30 in its axial direction.
Such a reduction gears-integrated actuator 30 has a structure in which the harmonic reduction gears 41, electric motor 34, and rotation position detector 52 are coupled to each other in a series in the axial direction in order from the load side to the anti-load side. Also, these devices are fixed inside hollow cylindrical actuator frames 31b, 31c and 31d, and both end portions are covered by the load side bracket 31a and the anti-load side bracket 31e. 
Of these, the harmonic reduction gears 41 are composed of a circular spline 42 which is fixed on the inner circumference of the actuator frame 31b, and at the same time is annular and has inner teeth, the flexible spline 43 which is attached to the inside of the circular spline 42, coupled to an output shaft 32, is cup-shaped and has outer teeth, and an elliptically shaped wave generator 44 which is attached to the inside of the flexible spline 43 via a bearing 47 and coupled to a rotation shaft 33. Also, the bearings 45 and 46 support the output shaft 32 and are given a preload by an elastic member 50. And, the bearings 48 and 49 support the rotation shaft 33 and are given a preload by an elastic member 51.
Further, the electric motor 34 is provided with a rotor 38 composed of a yoke 39 fitted to the rotation shaft 33 and a permanent magnet 40 that becomes a magnetic pole, and at the same time a stator 35 composed of a stator core 36 secured opposite to the outer circumferential side of the rotator 38 via a gap and an armature winding 37 that generates a rotation magnetic field at the stator core 36.
Further, the rotation position detector 52 is composed of an optical type encoder including a rotation disk 53 that becomes a rotation portion fixed at the rotation shaft 33, a fixed slit 54 that becomes a fixing portion of the rotation position detector, which is opposed to the rotation portion, a light emitting element 55, and a light receiving element 56. When light from the light emitting element 55 is projected onto the rotation disk 53, the light receiving element 56 repeats receiving and non-receiving of light via the fixed slit and detects the receiving and non-receiving of light as ON and OFF electric signals. After that, an angle of the rotor is calculated by a calculation circuit (not illustrated).
Next, a description is given of the actions thereof.
When a current flows from a drive circuit (not illustrated) into the armature winding 37 of the stator 35, a drive torque is generated in the permanent magnet 40 of the rotor 38, and the rotor 38 rotates at a high speed by the drive torque. Next, since the wave generator 44 coupled to the rotation shaft 33 of the rotor rotates, the flexible spline 43 is elliptically flexed via the bearing 47 and is engaged with the circular spline 42 at both end positions in the long axis direction of an ellipse in the wave generator 44. At this time, relative rotation is generated between the flexible spline 43 and the circular spline 42, wherein a remarkably reduced rotation force is transmitted from the flexible spline 43 to the output shaft 32 and is outputted therefrom.
However, in the prior art, since the harmonic reduction gears, electric motor and rotation position detector are coupled to each other in a line in a series, the length in the axial direction is made longer especially between the harmonic reduction gears and the electric motor, and between the electric motor and the rotation position detector. Further, the space of the rotation position detector disposed in the axial direction is increased, and this becomes a problem in view of downsizing and lightening of the weight thereof.
Also, since the harmonic reduction gears, electric motor and rotation position detector are, respectively, fixed at three actuator frames, the number of components is increased, resulting in an increase in the number of assembling steps, wherein another problem occurs, resulting in an increase in production costs thereof.
Further, there is a request for improving a torque capacity of an actuator in addition to a request of attempting downsizing and lightening of weight of the actuator. For this reason, it is necessary to make large the outer diameter of the rotor at a position where the permanent magnet thereof is installed, and to increase a drive torque of the rotor. However, in a structure in any of the prior arts, the outer diameter of the stator and actuator frame is increased if the outer diameter of the rotor is increased. Therefore, the cubic volume and weight of the entire electric motor are incidentally increased, and there is a problem which runs counter to the downsizing, lightening of weight and increasing of the torque in an actuator.
The present invention was developed to solve these and other problems, and it is therefore an object of the invention to provide an inexpensive reduction gears-integrated actuator that is capable of shortening the length of the entire actuator in its axial direction and increasing a drive torque without running counter to downsizing and lightening of its weight.
In order to solve the above-described problems, the invention is constructed as described below.
A reduction gears-integrated actuator according to the first aspect of the invention comprises a hollow cylindrical actuator frame; a circular spline that is fixed on the above-described actuator frame and has inner teeth on the inner circumference thereof; a cylindrical flexible spline that has outer teeth engageable with the inner teeth of the above-described circular spline, and has an output shaft of the actuator coupled to the end face thereof; a elliptical wave generator attached on the inner circumference of the above-described flexible spline; a rotation shaft for driving to rotate the above-described wave generator; an electric motor including a rotor provided with a magnetic pole consisting of a permanent magnet and stator provided with an armature winding for generating a rotation magnetic field at a stator core opposed to the outer circumferential side of the above-described rotor via a gap; a rotation portion of a rotation position detector fixed on the above-described rotation shaft; and a fixing portion of the rotation position detector, which is opposed to the rotation portion of the above-described rotation position detector; wherein the above-described rotor constitutes a cup-shaped rotation yoke integrally mounted at the center thereof so as to pass through the above-described rotation shaft, and at the same time fixes the above-described permanent magnet on the outer circumference of the above-described rotation yoke; the above-described circular spline is formed to be like a silk hat and at the same time, the cylindrical portion thereof is disposed so as to oppose the inner circumference of the above-described rotation yoke via a gap while the flange portion is fixed at one end portion of the above-described actuator frame; and the above-described circular spline is further provided, between the above-described output shaft and the above-described rotation shaft, with a cup-shaped housing coupled to the above-described output shaft on the inner circumferential side of the above-described flexible spline, a bearing that is fitted to the inside of the above-described housing and supports the above-described rotation shaft, and an elastic member that is provided in a gap in the axial direction between the above-described housing and the above-described bearing, and gives a preload to the above-described bearing.
Also, the reduction gears-integrated actuator according to the second aspect of the invention is constructed, in addition to the reduction gears-integrated actuator as set forth in the first aspect, so that the rotation portion of the above-described rotation position detector is composed of a disk-shaped magnet for detecting an angle, which is magnetized in a direction perpendicular to the above-described rotation shaft, and the fixing portion of the above-described rotation position detector is composed of a fixed ring provided on the outer circumferential side of the rotation portion of the above-described rotation position detector, and at least two magnetic sensors attached in the circumferential direction of the fixed ring.
Further, the reduction gears-integrated actuator according to the third aspect of the invention comprises a hollow cylindrical actuator frame; a circular spline that is fixed on the above-described actuator frame and has inner teeth on the inner circumference thereof; a cylindrical flexible spline that has outer teeth engageable with the inner teeth of the above-described circular spline, and has an output shaft of the actuator coupled to the end face thereof; a elliptical wave generator attached on the inner circumference of the above-described flexible spline; a rotation shaft for driving to rotate the above-described wave generator; an electric motor including a rotor provided with a magnetic pole consisting of a permanent magnet and stator provided with an armature winding for generating a rotation magnetic field at a stator core opposed to the inner circumferential side of the above-described rotor via a gap; a rotation portion of a rotation position detector fixed on the above-described rotation shaft; and a fixing portion of the rotation position detector, which is opposed to the rotation portion of the above-described rotation position detector; wherein the above-described rotor constitutes a cup-shaped rotation yoke integrally mounted at the center thereof so as to pass through the above-described rotation shaft, and at the same time fixes the above-described permanent magnet on the inner circumference of the above-described rotation yoke; the above-described circular spline is formed to be like a silk hat, and at the same time, the cylindrical portion thereof is disposed so as to be fixed at the inner circumference side of the above-described stator while the flange portion is fixed at one end portion of the above-described actuator frame; and the above-described circular spline is further provided, between the above-described output shaft and the above-described rotation shaft, with a cup-shaped housing coupled to the above-described output shaft on the inner circumferential side of the above-described flexible spline, a bearing that is fitted to the inside of the above-described housing and supports the above-described rotation shaft, and an elastic member that is provided in a gap in the axial direction between the above-described housing and the above-described bearing, and gives a preload to the above-described bearing.
Also, the reduction gears-integrated actuator according to the fourth aspect of the invention is constructed, in addition to the reduction gears-integrated actuator as set forth in the third aspect, so that the rotation portion of the above-described rotation position detector is composed of a disk-shaped magnet for detecting an angle, which is magnetized in a direction perpendicular to the above-described rotation shaft, and the fixing portion of the above-described rotation position detector is composed of a fixed ring provided on the outer circumferential side of the rotation portion of the above-described rotation position detector, and at least two magnetic sensors attached in the circumferential direction of the fixed ring.